Electronic and optical properties of ultra-small diameter armchair carbon and boron nitride nanotubes by PBE, TB-mBJ and YS-PBE0 functionals

Abstract

We have investigated the electronic and optical properties of ultra-small (3,3), (4,4) and (5,5) armchair single walled nanotubes carbon (C-SWNTs) and boron nitride (BN-SWNTs) using three density functional methods of different categories, namely, PBE, TB-mBJ and hybrid functional YS-PBE0. A density functional theory (DFT) within the full-potential linearized augmented-plane wave (FP-LAPW) method, was used to study the structures, electronic and optical properties of these nanotubes. The calculation of optical properties has been performed under electric fields polarized both parallel and perpendicular with respect to the nanotube axis. The results show that the hybrid functional YS-PBE0 perform the best for calculations of band gap of BN-SWNTs (5.27–5.54 eV), while for C-SWNTs the PBE and TB-mBJ functionals obtain band gap range (0.16–0.28 eV) with smaller errors compared to experimental values and confirming the semiconducting behavior of the studied C-SWNTs. The dielectric function is anisotropic for all tubes and is larger in the parallel direction. The results show also that for C-SWNTs, the static refractive index is higher than those of BN-SWNTs and it has an inverse correlation with the C-SWNTs diameter. This proves that for optoelectronic applications, it is improve to use the BN-SWNTs doped than intrinsic.